For many years Steve Rogers and Nick Fury were close allies in the comics. In fact, Steve requested to work directly with SHIELD and had many missions with the spy agency. All of Steve's wartime team, the Howling Commandos, ended up working with SHIELD as well (remember, the comics were written in the 1960s, when the Howlers could plausibly have survived and been young enough to still be active agents). Steve met Sharon Carter, his love interest and Peggy's sister (later niece) because Sharon was a SHIELD agent. Together, Captain America and SHIELD fought the resurgent HYDRA, his old nemeses from World War II.

With the close ties Captain America/Steve Rogers has traditionally had to SHIELD, it makes perfect sense that he would have a similar relationship with Fury's group in the MCU. I don't think that the movie will be any more crowded than CA:TFA was.

Unfortunately, the MCU is on a different timescale than the comics when it comes to WWII. Cap was only removed from Silver Age Marvel by less than two decades; MCU Cap is separated by *seventy* years. MCU Fury had nothing to do with WWII, obviously, and still wasn't even a gleam in his daddy's eye when Cap was out battling Red Skull. It's certainly conceivable that *Cap's* (MCU) Howling Commandos could have joined the SSR/proto-SHIELD after the war, but I don't know how many of them would have survived long enough to see Nick Fury join the team.

In the MCU, the friendship/partnership of Steve and Nick develops only in 2011, so it's only just beginning.